The design of rocket engine turbopumps is often limited by the materials used in the turbine section of the turbopump. The turbine blades of rocket engine turbines are subjected to high tensile vibratory and thermal stresses due to the high rotational speed of the turbine and the thermal gradients caused by the operating environment. These stresses are greatest at the root of the turbine blade and decrease at the tip of the blade. The turbine blade design and materials selection must provide adequate strength at the root of the blade to avoid blade failure during operation. The combustion gases entering the turbine are typically at a uniform temperature, and the turbine blades are therefore designed for the same thermal environment from the blade root to the tip. The life of a turbopump turbine is a function of the temperature at which it operates and the speed. One way to increase the operating life of a turbopump turbine is to manufacture the turbine blades from materials which are stronger at turbine operating temperatures than are those materials which are presently used in turbopump turbine blades. Accordingly, as such materials become available, they are typically incorporated into turbopump turbines to provide for longer turbine life or higher operating temperatures. However, materials development is a slow and expensive process. Prior art solutions to materials problems have been focused in two major areas: one is provide elaborate cooling schemes for turbine blades, and the other is to reduce the overall gas temperature entering the turbine from the combustion chamber. The former solution is expensive to apply, and is usually used as a last resort. The latter solution is not really a solution at all since temperatures must increase as engines become larger and efficiency requirements become more demanding.
What is needed is a method of increasing the operating life of a turbopump turbine using currently available materials without the necessity of providing additional cooling air or decreasing overall gas temperature entering the turbine from the combustion chamber.